Duplicating a cloth without rebaking?
Export the animation as .mdd file (enable export mdd addon in preferences). Choose the right fps and start and end frame of animation.
Now you can delete the cloth modifier from your flag object and delete all caches.
Add a Mesh Cache modifier to your flag and load the .mdd file with your animation.
Add a material slot and change it's link from Data to Object. Your flag copies will share the same mesh but will be able to have different materials.
Duplicate your flags with AltD. The Mesh Cache modifier will be copied to all the flags also.